Environmental Scan of the Namoi River Valley

Prepared for the Department of Land and Water Conservation and the

Namoi River Management Committee

December 1999

Martin Thoms

Richard Norris

John Harris

David Williams

Peter Cottingham

Environmental Scan of the Namoi River Valley

Prepared for the Department of Land and Water Conservation and the

Namoi River Management Committee

December 1999

Martin Thoms

Richard Norris

John Harris

David Williams

Peter Cottingham

Cooperative Research Centre for Freshwater Ecology

Ph:02 6201 5168

Fax:02 6201 5038

Email:

ISBN:0957704852

Environmental Scan of the Namoi River Valley

Executive Summary

The Department of Land and Water Conservation (DLWC) and the Namoi River Management Committee (NRMC) are currently developing a river management plan for the Namoi River and its tributaries. An assessment of the current biophysical condition of the Namoi River (environmental scan) is essential to develop a common understanding of the processes and management activities that affect the health of the river. This work, along with other socio-economic information, forms the basis for the development and implementation of the river management plan for the Namoi River.

This report of the environmental scan draws on previous investigations of the Namoi River system to identify the key ecological issues to be addressed in the river management plan, and important scientific knowledge gaps to be addressed in order to overcome barriers to, or improve the implementation of, management actions aimed at improving the ecological health of the river. The specific issues addressed are:

  • The importance of maintaining riverine health;
  • The nature of the catchment;
  • The level of knowledge of the biophysical condition of the Namoi;
  • Threats to riverine health along the Namoi;
  • A program to address scientific knowledge gaps.

A watershed or catchment focus is required for managing river health so that the interaction of landscapes, rivers and humans may be considered. Humans may alter the biological systems in a river by altering physical habitat, modifying seasonal water flow, changing the system’s food base, changing interactions among stream organisms, and contaminating the water with pollutants.

The connection of the riparian (stream bank) zone and floodplain with a river system is also important, as riparian vegetation and the floodplain provides organic matter (energy) and nutrients that drive primary production, and shade and refuge for biota such as fish. The linkage of rivers with their floodplains also helps maintain wetlands that are often important sources of local and regional biodiversity (e.g. populations of birds, fish and invertebrates).

The flow regime of a river plays a major role in river processes, as flow helps shape the river (affects geomorphology), provides cues for key biological processes (e.g. breeding cycles) and links the river with its floodplain. Flow regulation through dam and weir construction and water abstraction has led to severe stress being placed on many river ecosystems in the Murray Darling Basin, including the Namoi. Changes to flow and sediment regimes following catchment modification can markedly alter the physical nature of the channel and consequently the habitats that support organisms. We now recognise the need to allocate water to fulfil the needs of riverine environments and to protect these systems.

The health of a river may be assessed by comparing a site or area of interest with another thought to be in good condition (the reference condition). The reason for establishing reference conditions is to compare like with like. The approach most commonly used has been to select reference sites that are ‘minimally disturbed’. Often, pre-European disturbance conditions are set as restoration goals, but those conditions may not be attainable as this denies the place of humans in the landscape. In such circumstances, management targets should initially be set so they are achievable. A key aim should be to maintain the biological integrity of a system, that is “the ability of a system to support a balanced, integrated, adaptive community of organisms with a species composition, diversity and function comparable to that of natural habitat in the area”.

An assessment of the current condition of the Namoi identified the following as major contributors to the generally moderate to poor riverine condition that prevails:

  • Degradation of the riparian zone, or complete lack of riparian zone;
  • Channel morphology impacts such as bank instability, riverbed instability, and aggradation of sediments. This is primarily due to two factors: 1) excessive sand and gravel extraction, and 2) fluctuating water levels;
  • Morphological and biological effects of dams and river regulation;
  • Poor land management practices;
  • Poor water quality, mainly because of high total phosphorus, turbidity and salinity levels, and localised incidence of pesticide contamination;
  • Poor native fisheries, with low species diversity and abundance, especially in upland areas due to the presence of barriers to fish migration.

Seven river zones have been identified for the Namoi River system: pool, constrained, armoured, mobile, meander and distributary. A total of 23 major threats to river condition have been identified, with the anabranch, distributary and meander zones most at risk to environmental degradation. The alteration of river flows, clearing or absence of riparian vegetation, and threats resulting from land management activities (e.g. nutrient and pesticide transport to waterways) are threats common to each of the river zones. Addressing these threats is consistent with the aims and objectives of the Integrated Monitoring or Environmental Flows (IMEF) program, which is part of the NSW Water Reforms, and the recommendation of numerous reports on the state of natural resources in the Namoi River catchment. The NRMC has identified the following key issues to be addressed in their river management plan:

  • Fish passage;
  • Thermal pollution;
  • Floodplain management;
  • Off-allocation access;
  • Wetland status and other riparian vegetation;
  • Operation of dams and weirs;
  • Cultural and spiritual issues;
  • Carp reduction.

These issues are a mixture of ecological, water management and social-economic issues. In terms of managing environmental conditions, the above issues may be considered as part of two key questions:

  1. How do we maintain or improve native fish populations?
  2. How do we manage our river system to maintain or improve biodiversity and important functions such as riverine and wetland productivity?

Native fish populations are often used as an indicator of river health, as their presence is dependent on a number of factors such as energy (food) availability, water quality, flow regime and habitat availability. Maintaining biodiversity, and riverine functions such as production and respiration, are also important because they help maintain the resilience of ecosystems upon which we all ultimately depend; the connection of a river with its floodplain and floodplain wetlands is a key component in maintaining riverine health. Maintaining or improving the condition of Namoi River system is therefore dependent on the management of both in-stream and floodplain processes, and factors that threaten them.

Establishing a reference condition that serves as a target for future management in catchments that have been extensively modified (e.g. for agriculture) can be a difficult task, and will largely depend on the values attached to the riverine system by local communities. This can be achieved for in-stream conditions by the use of tools such as the Index of Biotic Integrity (based on fish populations) and AUSRIVAS modelling (based on macroinvertebrates). Both models use regional data sets to identify ‘reference’ sites where human impacts are considered minimal and conditions are indicative of healthy ecosystems. Comparison of the fish and invertebrate populations at test sites in the Namoi system with that expected to occur at reference sites can be used to establish the relative in-stream health of the Namoi. The reference sites may also serve as targets against which the effects of future management in the Namoi may be assessed.

While the IBI and AUSRIVAS are valuable tools for identifying in-stream reference conditions, no such formal tools are currently available for assessing riparian and floodplain conditions. Given that the riparian zone and the floodplain have been extensively modified and will often not be economically returned to their pre-development state, it is unrealistic to develop reference conditions based solely on pre-development (pre-European) conditions and use them as a target for future management. In this case, measures of intactness and functionality (e.g. length of stream with riparian vegetation that performs key ecosystem functions), or biodiversity and connectivity in key floodplain wetlands are likely to provide a guide to targets that may realistically be achieved or the result of best management practices.

In-stream priorities

The following recommendations are drawn from assessments of riverine condition and consideration of other factors:

  • The MacDonald River above Lowry is considered to be in excellent condition and may be considered as a reference site for upland streams in the Namoi. The maintenance of its condition should receive the highest priority in future management and restoration efforts.
  • Given its impact on biological and ecological function (e.g. breeding and growth of fish and macrophytes), a review of the extent and persistence of cold-water releases from major dams should be undertaken as soon as possible. This is especially important to ensure that future environmental flows are effective and that cold-water pollution does not prevent migratory fish from using fishways when installed.
  • The Peel and Cockburn Rivers are in relatively good condition, as is the Manilla River above Split Rock Dam, and should be given the next highest priority in management and restoration efforts. Important issues to be addressed include improving riparian zone condition, reducing the transport of nutrients from the catchments above Chaffey and Split Rock Dams that help sustain algal blooms, managing the salinity threat and managing the effects of stream instability resulting from sand and gravel extraction. The effectiveness of the fishway at Split Rock Dam should be evaluated and research undertaken to develop fishways for high dams such as Chaffey.
  • The priority given to the remaining rivers or river zones requires further consideration by the NRMC. Opportunities may exist to significantly improve the relative condition of rivers by addressing one or two factors (e.g. improved riparian condition along the Namoi River between the Manilla River confluence and Narrabri; effective fishways at Weeta, Gunindera and Mollee weirs). The effect of environmental flows should also be reviewed as recommended by the IMEF process, especially in terms of their effects on creeks, flood runners and wetlands in the lower Namoi distributary zone.

Floodplain priorities

Increased salinity is expected to continue as a major land and water management issue. The ecological effects of increased salinity have the potential to negate improvements achieved through management efforts such as the delivery of environmental flows and installation of fishways. Salinity management should continue to have a high priority in floodplain areas. While high stream salinity is already evident in the streams of the Liverpool Plains and areas of the Peel catchment, a review of trends in groundwater levels will be useful for identifying other areas at risk to salinity.

Surveys of the riparian condition should be undertaken to identify the remnant stands of intact vegetation in each of the major river zones. Existing high quality riparian vegetation should be protected as an example of realistically achievable conditions (future targets for improvement) and as natural seedbanks that will assist efforts for improving degraded riparian habitat.

The condition and biodiversity of key wetlands should be reviewed to provide a baseline to measure the effectiveness of future management, including environmental flows delivered through the NSW water reforms. Given their history in supporting a diversity or abundance of bird and fish populations, or habitat complexity, the following wetlands may be considered as part of this review: Lake Goran, and Gunnible, Gulligal, Barbers and Wirebrush Lagoons. Other wetlands may be added, depending on community priorities.

Assessing the effectiveness of the river management plan currently being prepared by the DLWC and NRMC will require a specifically designed monitoring and evaluation strategy such as the Integrated Monitoring of Environmental Flows (IMEF) program. With the establishment of this program in the Namoi Valley, particularly if the IMEF is further integrated with the Central and North West Regions Water Quality Program, a greater understanding of the linkages between catchment management practices and processes affecting water quality and biotic response to river flows may be achieved. Both the plan and associated monitoring and evaluation programs may be modified in the future as new information and insight becomes available (i.e. within an adaptive management framework).

Other areas of research that will provide valuable information for future riverine management include:

  • Biological control methods for carp as part of national efforts;
  • The effects of persistence of cold-water releases on fish, invertebrate and macrophyte biology;
  • Improved fishway design, especially for high dams.

Table of Contents

1INTRODUCTION......

1.1Background......

1.2Project Terms of Reference......

1.3Project Scope......

2THE IMPORTANCE OF MAINTAINING RIVERINE HEALTH......

2.1Why do we need healthy rivers?......

2.2How do rivers work?......

2.2.1Natural flows are variable......

2.2.2High flows feed rivers......

2.3Assessing River Health......

2.3.1Physical and chemical indicators......

2.3.2Biotic indicators......

2.4Why is a river management plan important?......

3The Namoi River Catchment......

3.1Catchment Character......

3.2River Geomorphology......

3.3Hydrology......

4THE CURRENT CONDITION OF THE NAMOI RIVER SYSTEM......

4.1Physical Condition......

4.2Physico-Chemical Water Quality Conditions......

4.3Biological Conditions......

4.3.1Invertebrates......

4.3.2Fish......

4.3.3Instream and Riparian Vegetation......

4.4Stream Condition Assessment......

4.5Summary of Condition......

5THREATS TO RIVER HEALTH......

5.1Current Threats and their Scientific Basis......

5.1.1Physical condition of the river channel......

5.1.2Riparian and aquatic vegetation......

5.1.3Fish......

5.2Emerging Threats......

5.2.1Water Quality......

5.2.2Riparian and aquatic vegetation......

5.2.3Fish......

5.3Prioritisation of Threats......

5.3.1Recommended DLWC and NRMC Priorities......

6PROGRAM TO ADDRESS SCIENTIFIC KNOWLEDGE GAPS......

6.1River Geomorphology......

6.2Water quality......

6.3Macroinvertebrates......

6.4Fish......

6.5Riparian Inventory and Priorities......

6.5.1Collation of existing knowledge of riparian systems......

6.5.2Vegetation and geomorphic survey of riparian zones......

7references......

Figures

Figure 1:Components of a river system......

Figure 2:Processes in upland rivers......

Figure 3:Processes in lowland constrained rivers......

Figure 4:River – floodplain interactions......

Figure 5:River zones in the Namoi catchment......

Figure 6:Long-term monthly flows (observed and simulated natural) for the Namoi River system: a) Peel River; b) Gunnedah, and c) Narrabri. Source: DLWC, Integrated Quantity and Quality Model (IQQM)

Figure 7:Namoi River Catchment Index of Stream Condition. * - Water Quality and Aquatic Life sub-indices could not be calculated.

Figure 8:Summary of key issues confronting riverine management in the Namoi catchment......

Tables

Table 1:Geomorphological zones of the Namoi Catchment......

Table 2:Total Annual Flow Statistics for the Namoi River (ML)......

Table 3:Changes in average return intervals of floods for selected sites in the Namoi River system. Source: DLWC, Integrated Quantity and Quality Model (IQQM)

Table 4: Characteristics of sites sampled in the Namoi River Catchment......

Table 5:Physical habitat assessment of sites in the Namoi River Catchment......

Table 6:Abundance of fish species recorded at sites in the Namoi River catchment. Data from the NSW Rivers Survey (Harris and Gehrke 1997). Surveys 1 – 5 occurred from October 1994 to April 1999.

Table 7.Summary of dominant riparian species in various reaches of the Namoi system (Source DWR 1992).

Table 8:Five-point scale for indicator measurements......

Table 9: Major threats to environmental condition of the 7 river regions in the Namoi......

Table 10:Interaction of effects associated with degrading influences......

Table 11: Combined assessment scores for sites across the Namoi catchment......

Table 12:Physical indicators of river system condition......

Glossary

Acute
Alien species
Alluvial
Anabranch
Antagonistic effect
AUSRIVAS
Benthic
Billabong
Biochemical
Biodiversity
Biological monitoring
Biophysical
Biota
Biotic (biological) integrity
Blue-green algae
Chronic
COAG
Concave
Consumptive uses
Cretaceous
DDT
Detritus
Devonian
Ecological function
Embeddedness
Environmental flows
Endosulfan
Fishways
Flow regime
Food webs
Geoindicators
Geomorphology
Habitat
Hydrology
IMEF
Index of Biotic Integrity
Index of Stream Condition
Invertebrate
Lateral extent
Landscape level
Leaf Litter
Macroinvertebrate
Macrophytes
Meander
Metamorphic
Metrics
ML
Organic material
Planforms
Planktonic
Primary production
Riffle
Riparian
RIVPACS
Secular change
Silurian
Spatial
Species diversity
Substratum
Surface waters
Taxa
Taxonomic richness
Temporal
Toxicant
Turbidity
Weir
Weir pool
Wetland / Sharp, short term
Native or introduced species not previously found in the area
Transported by water
A branch of a river that either rejoins the main stem or reaches a wetland
The tendency of processes or chemicals that together have a less powerful effect than when acting separately
A model developed in Australia to assess stream health based on macroinvertebrates
Living in or on the bottom sediments of a river, lake or wetland
A water hole or wetland formed from an old river channel
The chemistry of living organisms
The range of living organisms
The measurement of biological changes in an environment
The biological and physical components of an ecosystem
Plants and animals
The ability of a system to support a balanced, integrated, adaptive community of organisms with a species composition, diversity and function comparable to that of natural habitat in the area.
Algae-like organisms (Cyanobacteria) capable of photosynthesis
Long term
Council of Australian Governments
Curving inward, sunken
Used for drinking or preparing foods
Geological period from 135 until 70 million years ago
Pesticide previously used in agriculture
Decomposed plant or animal material
Geological period from 400 until 350 million years ago
Key function (e.g. primary production) upon which ecosystems are dependant
Extent to which physical features such as rocks are buried in sediment
Flows required to maintain key biological or ecological processes (e.g. breeding cycles in fish)
Insecticide used in agriculture
Structures built to enable fish to pass in-stream barriers such as weirs
Pattern of changes in flow in a river, lake or wetland
The network of food pathways in an ecosystem
Indicators of the geological state of a waterway or catchment
Study of the origin and character of land, rivers and lakes
An area used by an organism during its life cycle
The study of the behaviour of water
Integrated monitoring of environmental flows
A tool for measuring stream health based on fish populations
A tool for measuring the physical, chemical and biological state of rivers
An animal without a backbone
The extent of movement into the floodplain
Regional or catchment scale
Leaves, twigs and bark dropped by trees and shrubs into water
Animals without backbones that are visible to the naked eye
Plants that are visible to the naked eye
A twist in a river
Rock that has changed character in response to changes in temperature, pressure and chemical environment
Different measures of a particular characteristic (e.g. fish populations)
Megalitre or 1,000,000 litres
Material derived from living plants and animals
Aerial views of the shape of a river
Of microscopic plant and animals that float in the water column
Production of organic material by living organisms
Section of river with fast, shallow water over large sediments (e.g. rocks and stones)
Of the banks of a river or stream
A model developed in Britain to assess stream health based on macroinvertebrates
Periodic change
Geological period from 440 to 400 million years ago
Distance related
The range or number of species in a given area
The base material of a river, lake or wetland
Waters flowing or contained in rivers, lakes or wetlands
Plants or animals contained in discrete levels of a classification systems (e.g. family, genus, species)
The abundance of a particular taxa
Time related
Poison
Opaqueness of water
Small dam across a river
The area of water held behind a weir
An area that is permanently or temporarily inundated

Acknowledgements